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FIRST  EDITION 


PRINCIPLES  OF  COKING 

858 


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2-fO.A 


PRINCIPLES  OF  COKING 


THE  MANUFACTURE  OF  COKE 


DEFINITIONS  AND  GENERAL  PRINCIPLES 

1.  When  certain  bituminous  coals  are  heated  in  an 
enclosed  space  from  which  air  is  more  or  less  completely 
excluded,  the  volatile  matter  of  the  coal  is  first  driven  off  as 
a  dense  smoke,  while  the  main  mass  of  the  coal  fuses  and 
runs  together,  at  the  same  time  expanding  in  volume.  The 
passage  of  the  escaping  gases  through  the  plastic  mass 
causes  it  to  be  drawn  out  into  elongated  cells,  giving  it  a 
sponge-like  structure.  When  no  more  gases  are  evolved, 
there  remains  a  hard,  cellular,  dark-gray  residue,  consisting 
essentially  of  the  fixed  carbon  and  the  ash  of  the  coal, 
together  with  small  amounts  of  sulphur  and  phosphorus,  and 
usually  a  little  moisture  and  traces  of  unexpelled,  volatile, 
combustible  matter.  This  residue  is  called  coke,  and  the 
coal  is  said  to  be  coked.  Coke  is  better  adapted  for  certain 
metallurgical  purposes  than  the  coal  from  which  it  is  made. 

2.  Products  of  Coking. — The  products  of  the  coking 
process  are  solid  and  gaseous.  The  solid  products  are 
coke  and  ashes.  The  gaseous  products  are  the  moisture 
expelled  from  the  coal,  and  the  volatile  combustible  portions 
of  the  coal;  from  this  gaseous  product,  fuel  gas,  illuminating 
gas,  ammonia,  and  tar  may  be  separated.  The  products 
obtained  from  the  gases  are  called  by-products,  because  in 
the  ordinary  process  of  coking  the  gases  escape  into  the  air 
and  are  wasted,  or  at  most  are  used  only  for  fuel  purposes. 

Copyrighted  by  International  Textbook  Company.  Entered  at  Stationers'  Hall ,  London 


2  PRINCIPLES  OF  COKING  §68 

It  is  possible  to  save  these  by-products,  and  a  coking  plant 
at  which  they  are  saved  is  called  a  by-product  plant. 

Numerous  compounds  may  also  be  extracted  from  the  tar, 
such  as  oils,  medicinal  compounds,  and  the  so-called  coal- 
tar  colors;  but  as  the  extraction  of  these  is  carried  on  in  a 
chemical  manufactory  entirely  apart  from  the  coke  plant,  the 
term  by-products,  as  ordinarily  used  in  connection  with  coke 
making,  refers  simply  to  the  gas,  tar,  and  ammonia  water 
recovered  at  the  coke  plant. 

3.  Uses  of  Coke. — Probably  95  per  cent,  or  more  of  the 
coke  produced  in  the  world  is  used  in  blast  furnaces  or 
foundry  cupolas,  but  it  is  also  used  in  the  manufacture  of 
water  gas,  producer  gas,  and  as  a  domestic  and  locomotive 
fuel,  and,  in  general,  for  any  purpose  where  a  quick,  smoke¬ 
less  fuel  is  required.  Powdered  coke  is  used,  as  a  substitute 
for  graphite,  in  the  manufacture  of  foundry  facings  used 
on  the  inside  of  molds  in  making  castings;  for  surface-hard¬ 
ening  steel;  and  for  making  malleable-iron  castings  and 
arc-light  carbons. 

PROCESSES  OF  MANUFACTURE 

4.  Coke  is  made  in  open  pits  or  mounds,  in  beehive  or 
some  similar  form  of  oven,  in  retort  ovens,  or  in  gas  retorts. 
The  first  method  is  seldom  used  now,  except  to  test  samples 
of  coke  for  their  coking  qualities.  The  second  method, 
commonly  known  as  the  beehive  method ,  was,  until  recently, 
the  only  method  used  to  any  extent  in  the  United  States; 
and  while  it  is  still  the  prevailing  method,  the  third  method 
has  been  quite  extensively  introduced.  The  third  method, 
known  as  retort ,  or  by-product ,  coking ,  is  the  one  prevailing 
in  England  and  on  the  continent  of  Europe. 

5.  Open-Pit  Coking. — The  open-pit  method  of  making 
coke  is  illustrated  in  Fig.  1,  which  shows  a  perspective  sec¬ 
tional  view  of  an  open-pit  plant.  The  mounds  of  coal  to  be 
coked  are  described  indiscriminately  as  banks,  pits,  and  ricks, 
and  the  coke  made  as  bank  coke,  pit  coke,  and  rick  coke.  For 
the  purpose  of  making  pit  coke,  the  ground  is  leveled  for  a 


68 


PRINCIPLES  OF  COKING 


3 


width  of  14  feet  and  then  surfaced  with  coal  dirt  or  coke 
breeze,  preferably  the  latter  if  it  can  be  obtained.  On  this 
is  spread  a  layer  of  coal  18  inches  thick  and  as  long  as  the 
rick  is  to  be.  Cross-flues  a  6  inches  wide  and  10  inches  deep 
are  then  made,  as  shown,  by  piling  up  lumps  of  coal  or, 


Fig.  1 


better,  coke;  the  central  flue  b  is  made  12  inches  wide  and 
10  inches  deep  in  the  same  manner  as  the  side  flues.  At  the 
junction  of  the  center  and  side  flues,  a  central  flue  c,  which 
acts  as  a  chimney,  is  constructed  with  coarse  pieces  of  coke 
or  with  stones.  Dry  wood  is  placed  in  the  flues,  after  which 


4  PRINCIPLES  OF  COKING  §68 

they  are  covered  over  with  billets  of  wood;  coal  is  then  piled 
up  until  the  mound  is  completed,  as  shown. 

The  coking  of  the  mound  is  started  by  setting  fire  to  the 
kindling  wood  at  the  base  of  the  flue  c.  The  first  gases 
given  off  are  very  black  and  at  first  do  not  burn,  but  subse¬ 
quently  ignite  and  burn  freely.  The  success  of  the  process 
depends  on  keeping  the  fire  evenly  distributed  throughout 
the  mass,  a  matter  of  some  difficulty  in  loosely  constructed 
mounds  and  particularly  on  windy  days.  The  coke  burner 
should  entirely  or  partially  close  the  flues  on  the  most  freely 
burning  side.  The  smoke  changes  from  black  to  yellow  and 
then  to  light  blue,  and  when  the  blue  flames  (due  to  the  burn¬ 
ing  of  carbon  monoxide  to  carbon  dioxide)  appear  the  process 
is  completed.  This  requires  from  5  to  6  or  more  days.  The 
pile  is  gradually  covered,  as  the  coking  proceeds,  with  sod  or 
clay  from  the  bottom  upwards,  and  all  the  openings  stopped 
with  wet  coke  ashes.  After  cooling  for  4  or  5  days,  or,  on 
an  average,  on  the  tenth  day  after  the  initial  firing,  the  cover 
is  removed  in  places  and  the  coke  cooled  by  water  before 
drawing.  If  more  haste  is  necessary,  water  may  be  applied 
through  a  hose  down  the  flues.  This  water,  being  converted 
into  steam,  penetrates  the  mass  of  the  mound  and  soon 
extinguishes  any  fire.  The  yield  of  coke  in  such  pits  is 
small;  but  with  care  its  quality  is  excellent. 

6.  Beehive  coke  is  produced  in  a  hemispherical  brick 
chamber  called  a  beehive  oven  from  its  resemblance  to  the 
old  form  of  beehive.  The  initial  heat  for  each  charge,  after 
the  first,  is  supplied  by  that  remaining  in  the  walls  of  the 
oven  from  the  preceding  charge.  Before  an  oven  is  first 
charged,  the  walls  are  heated  up  for  several  days  by  means 
of  a  wood  or  coal  fire.  In  coking,  only  enough  air  is  admitted 
into  the  oven  to  furnish  oxygen  to  burn  the  combustible 
volatile  matter  drawn  off  from  the  coal  by  the  heat,  and 
the  combustion  of  this  volatile  matter  supplies  the  heat  for 
carrying  on  the  coking  process.  The  method  is  wasteful,  as 
some  of  the  fixed  carbon  is  always  consumed  and  no  attempt 
is  usually  made  to  recover  any  of  the  by-products.  Owing 


§68 


PRINCIPLES  OF  COKING 


5 


to  the  excellent  quality  of  the  product  made  in  beehive  ovens 
from  good  coking  coals,  and  to  the  comparative  cheapness 
of  the  plant,  this  process,  though  wasteful  of  the  products, 
is  widely  used. 

7.  Retort,  or  by-product,  coke  is  made  in  long, 
narrow,  upright  ovens  of  firebrick.  The  heat  is  supplied, 
from  start  to  finish,  by  the  combustion  of  a  portion  of  the 
volatile  matter  of  the  coal,  not  in  the  coking  chamber  itself, 
as  in  the  beehive  oven,  but  in  flues  in  the  walls  of  the  oven, 
or  in  a  special  combustion  chamber  from  which  the  intensely 
hot  gases  are  conveyed  through  the  passages  in  the  walls  of 
the  oven  proper. 

The  product  is  properly  called  retort-oven  coke ,  but  is  very 
frequently  known  as  by-product  coke ,  owing  to  the  fact  that 
when  such  ovens  are  used  the  by-products  are  generally 
saved.  The  coke  resulting  from  the  manufacture  of  illu¬ 
minating  gas  is  also  a  retort  coke. 

Any  coal  that  will  coke  in  the  beehive  oven  will  give  good 
results  in  the  retort  oven;  and  many  coals  that  will  not  coke 
in  the  beehive  oven  give  very  satisfactory  products  in  retorts. 
The  retort-oven  process  has  in  its  favor,  aside  from  making 
good  coke  from  coals  giving  poor  or  indifferent  results  in  the 
beehive  oven,  the  possible  and  usual  recovery  of  products 
otherwise  wasted  and  which  in  some  instances  have  a 
pecuniary  value  fully  equal  to  that  of  the  coke. 

The  details  of  the  manufacture  of  coke  in  beehive  or 
by-product  ovens  are  fully  given  in  Coking  in  Beehive  Ove?is, 
Parts  1  and  2,  and  By-Product  Coking,  Parts  1  and  2. 


COKING  COATS 

8.  The  term  coking  coal  is  usually  understood  in 
America  to  refer  to  coal  that  will  make  a  good  metallurgical 
coke  in  the  ordinary  beehive  oven.  The  general  meaning  of 
the  term  is,  however,  any  coal  from  which  a  good  metallur¬ 
gical  coke  can  be  obtained  in  any  practicable  form  of  coke 
oven.  Although  many  attempts  have  been  made  to  determine 


6  PRINCIPLES  OF  COKING  §68 

what  is  essential  to  a  coking  coal,  it  is  not  known  why  cer¬ 
tain  coals  will  coke  and  others  will  not. 

9.  The  term  cement,  or  binder,  is  often  applied  to  the 
substance  or  substances  in  coal  on  which  the  coking  property 
seems  to  depend.  The  composition  and  nature  of  this 
binder  have  never  been  determined,  and  indeed  it  is  not 
definitely  known  that  it  is  a  distinct  substance,  as  the 
property  of  coking  may  depend  on  certain  physical  proper¬ 
ties.  Since,  however,  certain  coals  coke  and  others  do  not, 
and  certain  coals  coke  in  the  beehive  oven  and  others  do 
not,  but  can  be  coked  in  a  retort  oven,  there  is  a  difference 
between  coals;  and  for  want  of  a  better  term  to  explain 
this  difference,  the  substance  in  the  coal,  or  the  property 
of  the  coal  on  which  the  difference  depends,  is  known  as 
the  binder,  or  cement. 

Although  it  is  not  possible  to  determine  exactly  on  what 
the  coking  of  a  coal  depends,  certain  conclusions  based  on 
observation  have  been  reached,  which  are  useful  in  deter¬ 
mining  the  probability  of  a  coal  being  a  coking  coal.  Sub¬ 
sequent  and  more  extended  observations  may  prove  many  of 
these  conclusions  to  be  incorrect. 


CHEMICAL  COMPOSITION  OF  COKING  COALS 

10.  Various  attempts  have  been  made  to  explain  the 
coking  and  non-coking  of  various  coals  from  the  chemical 
compositions  of  the  coals — as,  for  instance,  the  relation 
between  the  fixed  carbon  and  the  volatile  matter,  or  between 
hydrogen  and  oxygen,  etc. — but  such  attempts  have  failed, 
for  one  coal  may  coke  well  while  another  of  about  the  same 
chemical  composition  may  not  coke  at  all. 

Table  I  gives  analyses  of  some  typical  coking  coals. 

11.  Volatile  Matter. — Attempts  to  explain  the  coking 
or  non-coking  of  coals  by  the  amount  of  volatile  matter  they 
contain  or  by  the  ratio  between  the  amount  of  volatile  matter 
and  the  other  ingredients  in  the  coal,  have  failed,  since  coals 
yielding  good  coke  range  all  the  way  from  13  to  40  per  cent, 
in  volatile  matter. 


§68 


PRINCIPLES  OF  COKING 


7 


Although  coals  extremely  high  in  volatile  matter,  such, 
for  example,  as  cannel,  can. rarely  be  coked  in  their  natural 
state,  at  least  in  present-day  ovens,  it  is  possible  that  some 


TABLE  I 


Locality 

Chemical  Composition  of  Coking  Coals 

Remarks 

Moisture  212°  F. 
Per  Cent. 

Volatile  Matter 
Per  Cent. 

Fixed  Carbon 
Per  Cent. 

Ash 

Per  Cent. 

Sulphur 

Per  Cent. 

Phosphorus 

Per  Cent. 

Pennsylvania: 

Connellsville  .  . 

1.86 

30.12 

59.61 

8.41 

.78 

.024 

Best  coking 

Broad  Top  .  .  . 

1.28 

18.40 

71.12 

7-50 

1.70 

Trace 

Good  coking 

Bennington  .  .  . 

1.20 

23.68 

68.77 

5-73 

.62 

.017 

Good  coking 

Johnstown  .  .  . 

.72 

16.49 

73-84 

7-97 

I.97 

Dry  coking 

Greensburg  .  .  . 

1 .02 

33-50 

61.34 

3.28 

.86 

Good  coking 

Armstrong  Co.  . 

.96 

38.20 

52.03 

5-i4 

3-66 

Pitchy  coking 

West  Virginia: 

7 

Pocahontas  .  .  . 

1. 01 

18.81 

72.71 

5*191 

OO 

Best  coking 

Fairmont  .... 

1.50 

36.70 

54-80 

7.00 

2.10 

Alabama: 

Birmingham  .  . 

2.10 

25-77 

68.35 

3-70 

.07 

Brookwood  .  .  . 

1-75 

24-15 

65.55 

8-55 

1.40 

Gamble . 

2.78 

24.67 

61.96 

10^59 

•43 

Tennessee: 

Jellico . 

4.40 

3I-56 

61.87 

1.86 

.31 

Briceville  .... 

•57 

30.41 

63.04 

3.62 

.23 

Illinois: 

Mt.  Carbon  .  .  . 

2.08 

38.20 

53-47 

8.02 

.63 

.027 

Pitchy  coking 

Colorado: 

El  Moro  .... 

•95 

29.82 

56.41 

12.82 

.41 

Good  coking 

Crested  Butte  .  . 

.72 

23-44 

71.91 

3-93 

•36 

Good  coking 

Mexico: 

Coahuila  Coal  Co. 

1 .60 

15.00 

'67.64 

12.01 

.86 

preliminary  treatment  might  render  them  adaptable,  though 
of  course,  owing  to  their  small  content  of  fixed  carbon,  the 
yield  of  coke  would  necessarily  be  small. 


8 


PRINCIPLES  OF  COKING 


§68 


12.  An  unsatisfactory  classification  of  coals  based  on  the 
volatile  contents  is  sometimes  given  as  follows:  A  rich 
coking  coal  contains  from  35  to  40  per  cent,  of  volatile  matter 
and  produces  a  spongy  open  and  soft  coke.  These  coals 
require  a  moderate  degree  of  heat  to  coke  them,  and  seem  to 
contain  an  excess  of  cement  or  binding  material  and  to 
require  its  partial  expulsion  by  moderate  heat  before  the 
actual  coking  begins.  Normal  coking  coals  contain  from  25 
to  35  per  cent,  of  volatile  matter;  in  Connellsville  coal  a 
content  of  about  32  per  cent,  is  generally  accepted  as  a 
standard.  These  coals  give  equally  good  results  in  any  kind 
of  oven.  Dry  coking  coals  are  those  containing  20  to  25  per 
cent,  of  volatile  matter.  Many  coals  with  this  amount  of 
volatile  matter  will  not  give  a  good  hard  coke  in  the  beehive 
oven,  but  will  coke  satisfactorily  in  the  retort  oven;  on  the 
other  hand,  some  of  the  best  coking  coals,  such  as  the  Poca¬ 
hontas,  contain  only  about  20  per  cent,  of  volatile  matter. 

13.  Fixed  Carbon. — Some  coals  low  in  fixed  carbon 
and  normally  non-coking  may  be  made  to  coke  by  mixing 
them  with  pitch  or  tar,  which  seems  to  supply  the  binder 
otherwise  lacking. 

14.  Moisture. — Coals  containing  a  small  percentage  of 
water  when  freshly  mined  are  generally  coking,  while  those 
that  contain  a  high  percentage  of  water  when  freshly  mined 
are  seldom  or  never  coking  coals.  For  example,  five  coals 
ranging  from  7.77  to  9.99  per  cent,  in  moisture,  with  an 
average  of  7.93  per  cent.,  were  non-coking;  while  coals  con¬ 
taining  from  1.72  to  1.98  per  cent,  were  coking.  The  Cre¬ 
taceous  and  Tertiary  coals  of  the  West,  running  as  high  as 
15  or  more  per  cent,  moisture,  do  not  usually  coke;  but  where 
for  any  reason  the  moisture  has  been  reduced  to  a  small 
amount,  by  metamorphic  action  for  example,  the  coal  will 
frequently  coke.  Local  or  regional  metamorphism  may,  and 
probably  does,  affect  other  constituents  than  the  moisture, 
but  the  fact  remains  that  coals  very  high  in  moisture  do  not 
usually  coke  in  a  beehive  oven. 


§68 


PRINCIPLES  OF  COKING 


9 


15.  Ash. — Within  very  wide  limits,  the  amount  of  ash 
has  no  effect  on  the  coking  qualities  of  coal.  Coals  ran¬ 
ging  from  3  per  cent,  to  20  per  cent,  in  ash  will  coke,  yield¬ 
ing  a  product  varying  approximately  from  4.5  per  cent,  to 
30  per  cent,  in  ash.  Naturally,  every  unit  of  ash  displaces 
one  of  fixed  carbon,  thus  lessening  the  heating  power  of 
the  coke.  It  is  claimed  by  many  that  a  certain  amount  of 
ash  is  essential  to  a  good  coke,  giving  the  desired  strength 
to  the  cell  walls;  and  the  statement  is  made  that  a  coke 
carrying  from  10  to  11  per  cent,  of  ash  is  harder  and  stronger 
than  one  containing  from  6  to  7  per  cent. 

16.  Sulphur. — The  amount  of  sulphur  that  a  coking  coal 
can  contain  depends  on  the  amount  of  sulphur  that  the  result¬ 
ing  coke  can  contain  and  still  be  salable.  No  amount  of  sul¬ 
phur  in  a  coal  up  to  this  point  affects  its  coking  properties. 
Sulphur  is  to  some  extent  volatilized  during  coking;  but  since 
it  takes  approximately  li  tons  of  coal  to  make  a  ton  of  coke, 
the  coke  usually  contains  about  the  same  percentage  as  the 
coal  from  which  it  is  made;  that  is,  if  the  coal  contains  1  per 
cent,  of  sulphur,  the  coke  will  contain  1  per  cent.  This  is  an 
approximate  rule  only,  and  some  cokes  contain  less  sulphur 
than  the  coal  from  which  they  were  made;  others  contain  more. 

Sulphur  exists  in  coal  in  several  forms:  first,  as  iron 
pyrites  or  sulphide  of  iron,  FeS2;  second,  as  gypsum  or 
calcium  sulphate;  third,  as  organic  sulphur  combined  with 
carbon,  oxygen,  and  hydrogen.  Some  authorities  also  give 
a  fourth  form  as  free  sulphur. 

If  sulphur  is  present  as  iron  pyrites,  a  considerable  amount 
(about  one-half)  is  driven  off  in  coking;  but  if  present  as 
gypsum,  none  is  removed.  In  fourteen  coals  examined  by  one 
chemist,  the  average  percentage  of  sulphur  was  1.591,  of  which 
1.152  was  in  combination  with  iron  and  .439  existed  “free.” 
The  sulphur  contained  in  the  resulting  cokes  amounted, 
on  an  average,  to  .952  per  cent,  of  the  sulphur  of  the  coal, 
showing  an  expulsion  of  40.16  per  cent,  of  the  total  sulphur 

during  coking,  since  A-591  .952\  iqq  _  jg  per  cenj-. 

\  1.591  / 


10 


PRINCIPLES  OF  COKING 


§68 


These  results  seem  to  show  that  all  the  “free”  sulphur 
does  not  pass  off  with  the  volatile  matter  in  the  process  of 
coking,  as  is  often  supposed.  In  twenty-five  coals  examined 
by  the  same  person,  the  percentage  of  sulphur  expelled  by 
coking  varied  from  57.92  to  14.75  per  cent.,  the  average 
being  38.50  per  cent. 

Various  unsuccessful  experiments  have  been  made  to 
reduce  the  sulphur  in  coke  by  mixing  the  coal  with  salt, 
lime,  or  other  chemicals  before  charging  it  into  the  oven. 
If  present  as  pyrites,  the  sulphur  can  be  greatly  lessened  by 
passing  the  fine  coal  through  some  one  of  the  various  wash¬ 
ing  machines.  The  attempts  to  remove  sulphur  from  coke 
before  its  use,  by  heating  in  air  or  oxygen  at  and  above 
atmospheric  pressure,  have  not  proved  successful;  in  every 
case,  a  portion  of  the  fixed  carbon  was  consumed,  with  a 
corresponding  increase  in  the  percentage  of  ash.  Where, 
therefore,  a  careful  handling  and  subsequent  washing  of  the 
coal  will  not  remove  the  excess  of  sulphur,  it  is  scarcely  to 
be  hoped  that  this  can  be  accomplished  in  the  coke  ovens. 

17.  Phosphorus  is  not  removed  in  the  process  of 
coking  and  is  concentrated  in  the  coke.  It  cannot  usually  be 
reduced  in  amount  by  a  preliminary  washing.  The  greater 
part  of  the  phosphorus  sometimes  occurs  in  a  certain  section 
of  a  coal  seam,  in  which  case  the  percentage  of  phosphorus 
in  the  coke  may  be  kept  down  by  coking  only  a  portion  of  the 
seam.  For  instance,  in  the  Pittsburg  seam  from  which  the 
celebrated  Connellsville  coke  is  made,  the  amount  of  phos¬ 
phorus  increases  gradually  from  bottom  to  top  of  the  seam; 
hence,  the  best  coke  is  made  from  coal  taken  from  the  bottom 
part  of  this  seam.  The  coking  properties  of  the  coal  do  not 
seem  to  depend  in  any  way  on  the  amount  of  phosphorus 
contained. 

18.  Foreign  Substances. — Foreign  substances,  such  as 
lime  and  lime  feldspar,  which  sometimes  occur  in  the  cleats 
of  a  coal  bed,  seem  to  render  a  coal  non-coking;  while  the 
same  coal  without  the  feldspar  may  coke.  The  Northumber- 
land-Durham  field  in  England  illustrates  this  point.  On  the 


§68 


PRINCIPLES  OF  COKING 


11 


northern,  or  Northumberland,  side  of  the  fault  dividing  the 
coal  basin,  the  majority  of  the  seams  have  their  cleats  filled 
with  plates  of  lime  feldspar  from  tV  inch  to  }  inch  thick, 
while  on  the  southern,  or  Durham,  side  this  feldspar  is 
almost  entirely  wanting.  Both  fields  supply  coking  coals, 
the  larger  number  and  better  quality  from  the  Durham,  but 
in  each  instance  it  is  only  the  coals  that  do  not  have  the 
feldspar  that  coke.  If  the  fine  coal  is  washed  and  separated 
from  the  feldspar  and  other  impurities,  a  fair  coke  may  be 
made  from  the  cleaned  slack  that  results,  indicating  that  the 
feldspar  prevents  the  coking  of  the  coal. 


GEOLOGICAL  POSITION  OF  COKING  COALS 

19.  The  geological  position  of  a  coal  seems  to.  have 
little  or  no  effect  on  its  coking  properties.  Any  coal, 
whether  belonging  to  the  Upper  or  Lower  Carboniferous, 
Triassic,  Jurassic,  Cretaceous,  or  even  Tertiary  Age,  may 
coke  if  properly  treated,  or  it  may  not;  but  certain  forma¬ 
tions,  such  as  the  Carboniferous,  are  more  apt  to  yield  good 
coking  coals  than  others.  Again,  certain  portions  of  a  given 
formation  may  contain  better  coking  coals  than  another  part, 
as  in  the  Clyde  basin  in  England,  where  all  the  seams  in  the 
upper  coal  measures  are  non-coking,  and  all  in  the  limestone 
series,  or  lower  coal  measures,  are  coking.  In  a  more  limited 
sense,  a  certain  coal  of  a  certain  formation  may  coke  wher¬ 
ever  found,  or  it  may  coke  in  one  portion  of  the  field  and  not 
in  another.  The  coal  from  one  bed  may  coke,  while  that 
from  another  bed  only  a  few  feet  above  or  below  it  may  not. 
All  that  can  be  gathered  from  geological  position  is  that 
certain  seams  of  certain  formations  will  probably  yield  better 
coke  than  other  seams  in  the  same  or  other  measures. 


PHYSICAL  PROPERTIES  OF  COKING  COALS 

20.  Texture. — The  effect  of  texture  on  the  coking 
qualities  of  a  coal  may  be  considered  in  a  twofold  light: 
first,  as  the  coal  occurs  in  place  in  the  mine;  and  second,  as 
it  is  charged  into  the  ovens. 


12 


PRINCIPLES  OF  COKING 


§68 


The  structure  of  the  coal  in  place  in  the  mine  seems  to 
have  little  or  no  effect  on  its  coking-  quality,  and  a  soft  mushy 
coal  and  a  hard  columnar  or  blocky  coal  may  make  equally 
good  coke  when  properly  treated. 

21.  The  condition  of  the  coal  when  charged  into  the  oven 
may  and  usually  does  have  a  marked  effect  on  the  coke  pro¬ 
duced.  Although  good  coking  coal  will  usually  make  good 
coke  when  charged  as  run  of  mine,  it  will  usually  make 
better  coke  when  charged  in  the  form  of  slack. 

Certain  coals  that  will  not  coke  in  lump  form  make  excel¬ 
lent  coke  when  ground  to  slack.  All  coals,  even  of  the  high¬ 
est  coking  qualities,  give  better  results  when  charged  evenly 
sized.  The  reason  for  this  seems  to  be  that  the  fine  condi¬ 
tion  of  the  coal  permits  the  more  rapid  evolution  of  gas  from 
the  increasing  number  of  surfaces  exposed  to  the  action  of 
heat;  the  fusing  or  melting  of  the  pitch-like  constituents  of 
the  coal  is  more  complete;  and  the  gas  more  readily  and 
easily  forces  its  way  through  the  fused  mass,  producing  the 
open  cellular  structure  essential  to  good  coke.  The  impor¬ 
tance  of  a  preliminary  crushing  is  more  marked  with  coals 
low  in  volatile  matter  than  with  others.  In  these,  the  slack 
fuses  and  cokes  first  and  often  only  the  surface, of  the  lumps 
is  coked,  the  coal  in  the  center  being  merely  charred.  As  a 
general  rule,  the  lower  in  volatile  matter,  the  finer  should  be 
the  coal  to  give  the  best  coke. 

On  the  other  hand,  the  coking  qualities  of  certain  light 
coals  may  be  increased  by  subjecting  the  slack  to  a  prelimi¬ 
nary  compression  and  charging  the  coal  in  artificial  lumps. 
This  is  done  in  Germany  in  preparing  otherwise  non-coking 
coals  for  use  in  retort  ovens. 

•  „ 

22.  Effect  of  Weathering;.  —When  coal  is  exposed  for  a 
length  of  time  to  ordinary  atmospheric  moisture  and  heat,  its 
coking  qualities  are  generally  wholly  or  partially  destroyed. 
The  fact  is  of  importance  in  showing  that  freshly  mined 
coal  should  be  coked  at  once,  and  has  a  bearing  in  sampling 
a  coal  field  for  its  coking  properties.  Ordinarily,  samples 
are  taken  where  the  coal  has  been  more  or  less  weathered, 


68 


PRINCIPLES  OF  COKING 


13 


and  it  must  be  borne  in  mind  that  experimental  lots  of  coke 
made  therefrom  will  not  be  equal  to  that  made  when  the 
plant  is  constructed  and  mining  under  normal  conditions. 

23.  Effect  of  Process  and  Temperature. — Coking 
depends  on  the  temperature;  if  this  is  low  and  slowly 
applied,  the  volatile  matters  are  expelled  without  fusion  and 
no  coke  results;  on  the  other  hand,  if  the  heat  is  high  and 
rapidly  applied,  the  coal,  if  of  the  coking  class,  will  coke.  The 
effect  of  process  and  temperature  on  the  quality  of  the  coke 
should  be  considered  together,  since  the  main  difference 
between  the  two  chief  processes,  beehive  and  retort,  con¬ 
sists  in  the  way  of  applying  the  heat  in  the  two  processes. 
In  the  beehive,  the  temperature  is  at  first  quite  low  and 
slowly  increases  until,  toward  the  end  of  the  process,  the 
maximum  is  reached.  The  heat  also  comes  mainly  from 
one  side  of  the  charge.  In  the  retort,  the  temperature  is 
more  nearly  the  same  from  beginning  to  end,  and  is  applied 
to  the  charge  from  all  sides.  The  first  is  a  slow  process; 
the  latter,  rapid. 

Other  things  being  equal,  within  certain  limits,  the  higher 
the  temperature  of  the  oven,  the  greater  will  be  the  yield. 
This  is  shown  by  the  fact  that,  if  an  oven  is  charged  at  once 
after  drawing  and  before  it  has  time  to  cool,  t*he  yield  is 
much  greater  than  if  it  is  allowed  to  stand  empty  for  several 
hours  with  the  door  open. 

The  higher  the  temperature  of  the  oven  and  the  longer  the 
coal  is  exposed  to  the  heat  of  the  oven,  the  harder  and  more 
dense  is  the  coke. 


YIELD  OF  COKE 

-  24.  The  theoretical  yield  of  coke  from  any  coal  is 
obtained  by  adding  together  the  percentages  of  the  solid 
parts  of  the  coal,  the  fixed  carbon,  and  the  ash,  as  given  by 
^proximate  analysis.  The  theoretical  yield  is  not  generally 
reached  in  beehive-oven  practice,  as  some  of  the  fixed  carbon 
is  burned  during  the  process  of  coking;  it  may,  however,  be 
exceeded  in  retort-oven  practice. 


14 


PRINCIPLES  OF  COKING 


§68 


Assuming  a  coking  coal  to  contain: 

Per  Cent. 

Moisture .  1.20 

Volatile  combustible  matter  31.50 

Fixed  carbon .  59.801  67.3  per 

Ash .  7.50 J  cent,  coke 

Total . 100.00 

Sulphur .  .80 

Phosphorus .  .006 

the  theoretical  yield  would  be  67.3  per  cent,  of  the  coal 
charged  into  the  oven. 

Coking  coals  with  sufficient  volatile  matter  to  supply  the 
heat  required  in  the  process  of  coking  will  approximate  more 
closely  to  the  theoretical  yield  than  coals  containing  a 
smaller  amount  of  volatile  matter  and  where  the  deficiency 
has  to  be  made  up  by  the  burning  of  a  portion  of  the  fixed  car¬ 
bon.  This  loss  of  carbon  is  sometimes  made  up  by  the 
decomposition,  at  a  high  temperature,  of  some  of  the  volatile 
hydrocarbons  and  the  deposition  of  some  of  the  carbon  on 
the  coke. 

In  the  Connellsville  region,  the  yield  of  coke  is  nearly 
equal  to  the  theoretical  yield,  which,  according  to  the  analysis 
given  in  Table  I.  is  about  66f  per  cent,  of  the  weight  of  the 
coal.  It  therefore  requires  if  tons  of  Connellsville  coal  to 
make  1  ton  of  coke  ( 100  --  66f  =  li) .  In  the  Pocahontas  field, 
however,  although  the  theoretical  yield  of  coke,  as  given  by 
Table  I,  is  greater  than  in  the  Connellsville  region  (being 
about  77  per  cent.),  the  actual  yield  of  coke  is  only  from 
58  to  61  per  cent,  of  the  weight  of  the  coal  coked.  This 
difference  in  yield  is  due  to  the  smaller  amount  of  volatile 
matter  in  Pocahontas  coal,  requiring  that  a  larger  amount  of 
the  fixed  carbon  be  burned  in  the  oven  to  furnish  the  heat 
to  coke  the  coal.  According  to  the  figures  here  given,  it 
requires  If  tons  of  Pocahontas  coal  (100  -f-  60  =  if)  to  pro¬ 
duce  1  ton  of  coke. 

25.  When  coal  is  coked  in  a  retort,  the  yield  of  coke 
generally  exceeds  the  theoretical  yield  calculated  by  the 


§68 


PRINCIPLES  OF  COKING 


15 


method  given  in  Art.  24.  The  amount  of  this  increase  varies, 
but  is  usually  from  5  to  10  per  cent.  This  increase  is  due 
to  the  decomposition  at  a  high  temperature  of  the  hydro¬ 
carbon  gases  contained  in  the  volatile  combustible  matter 
of  the  coal  and  the  deposition  of  the  carbon  on  the  coke,  and 
also  to  the  fact  that  none  of  the  carbon  of  the  coal  is  burned 
in  the  retort  to  furnish  heat  for  the  coking  process,  as  is  the 
case  in  the  beehive  oven.  The  yield  of  coke  in  a  by-product 
oven  is  frequently  75  per  cent,  of  the  weight  of  the  coal 
coked  when  the  theoretical  amount  of  coke  in  the  coal  is  only 
about  66  per  cent.  If  the  yield  is  75  per  cent.,  it  will  require 
li  tons  (100  -r-  75  =  li)  of  coal  to  produce  1  ton  of  coke. 

26.  Approximate  Composition  of  Coke. — If  the 
proximate  analysis  of  a  coking  coal  and  the  number  of  tons 
required  to  make  a  ton  of  coke  are  known,  the  approximate 
analysis  of  the  coke  may  be  determined  as  follows: 

Rule  I. — Multiply  the  percentage  of  ash  in  the  coal  by  the 
number  of  tons  of  coal  required  to  make  a  ton  of  coke;  the  product 
will  be  the  amount  of  ash  in  the  coke. 

Rule  II. — The  percentage  of  fixed  carbon  in  the  coke  is  then 
obtained  by  subtracting  the  amount  of  ash  from  100  per  cent. 

This  approximation  neglects  the  amount  of  sulphur  and 
phosphorus  in  the  ash  of  the  coal,  and  also  any  small  amounts 
of  moisture  and  volatile  matter  in  the  coke,  but  is  close 
enough  to  give  a  general  idea  of  the  composition  of  the 
coke.  The  percentage  of  sulphur  in  the  coke  is  assumed  to 
be  the  same  as  in  the  coal.  (See  Art.  16.) 

Rule  III. — The  percentage  of  phosphorus  in  the  coke  is  obtained 
by  multiply  big  the  percentage  of  phosphorus  in  the  coal  by  the 
number  of  tons  of  coal  required  to  make  1  ton  of  coke. 

The  application  of  these  rules  is  shown  by  the  following 
example: 

.  Example. — Calculate  the  approximate  composition  of  cokes  made  in 
the  beehive  and  by-product  ovens  from  the  coal  of  which  an  analysis 
is  given  in  Art.  24. 


16 


PRINCIPLES  OF  COKING 


§68 


Solution. —  Beehive  Coke  Retort  Coke 

Ash .  7.5  X  1.5  =  11.25  7.5  X  H  =  10.00 

Fixed  carbon  (by  difference)  88.75  90.00 

100.00  100.00 

Sulphur .  .80  .80 

Phosphorus  .  .  .  .006  X  1.5  =  .009  .006  X  l£  =  .008 


27.  A  slightly  more  accurate  method  is  sometimes  used, 
in  which,  in  the  analysis  of  the  coal,  the  percentages  of  sul¬ 
phur  and  phosphorus  are  given  separately  from  the  per¬ 
centage  of  ash.  In  calculating  the  theoretical  yield  of  coke, 
the  fixed  carbon,  ash,  one-half  the  sulphur,  and  all  the  phos¬ 
phorus  are  added.  Thus,  if  the  approximate  analysis  of  a 
coal  is: 

Per  Cent. 


Volatile  matter .  34.79 

Fixed  carbon  .  57.86 

Ash  (without  sulphur  and  phosphorus)  .  .  6.19 

Sulphur .  1.144 

Phosphorus .  .016 

Total .  100.000 


the  theoretical  yield  of  coke  will  be  57.86  +  6.19  +  .572  (i  of 
1.144)  +  .016  =  64.638.  It  therefore  requires  100  -r-  64.638 
—  1.54  tons  of  coal  to  make  1  ton  of  coke. 


28.  To  Calculate  the  Gain  or  Loss  in  Fixed  Carbon. 
If  the  analyses  of  a  coal  and  of  the  resulting  coke  are  known, 
the  loss  or  gain  in  fixed  carbon  over  the  theoretical  amount 
determined  as  above  may  be  calculated  as  shown  below, 
the  following  analyses  having  been  given: 


Per  Cent.  Per  Cent. 


Volatile  matter . 

Fixed  carbon . 

Ash  (without  sulphur  and  phos¬ 
phorus)  . 

Sulphur . 

Phosphorus  . 


in  Coal 

in  Coke 

•  34.79 

0.00 

57.86 

89.20 

6.19 

9.50 

1.144 

1.276 

.016 

.024 

100.000 

100.000 

Total  . 


§68 


PRINCIPLES  OF  COKING 


17 


As  was  calculated  in  Art.  27,  it  will  take  1.54  tons  of  this 
coal  to  make  1  ton  of  coke.  Then,  the  theoretical  fixed 
carbon  in  1  ton  of  coke  should  be  57.86  X  1.54  =  89.10  per 
cent.,  but  as  the  analysis  of  the  coal  shows  89.20  per  cent., 
there  is  evidently  a  slight  gain  in  carbon.  Similarly,  for  the 

sulphur  X  1-54  =  .88  per  cent,  sulphur,  while  the 

analysis  of  the  coke  shows  1.276  per  cent.  This  shows  that 
the  assumption  made  in  Art.  27  that  one-half  of  the  sulphur 
goes  into  the  coke  is  not  as  accurate  as  the  assumption  made 
that  the  amount  of  sulphur  in  the  coke  is  about  the  same 
as  in  the  coal.  (See  Art.  26.)  For  the  ash,  6.19  X  1.54 
=  9.53  percent.,  which  is  very  close  to  the  percentage  given 
by  analysis.  _ 


VARIETIES  OF  COKE 

29.  According  to  the  length  of  time  that  the  charge  of 
coal  remains  in  the  oven,  the  resulting  coke  is  called  24-,  48-, 
or  72-hour  coke.  Different  varieties  of  coke  are  also  named, 
from  the  uses  to  which  they  are  put,  as  follows: 

Furnace  coke  and  foundry  coke  are,  as  their  names 
imply,  used  respectively  in  producing  pig  iron  in  the  blast 
furnace  and  melting  the  same  in  the  foundry  cupola. 

Gas-house  coke  is  the  residue  remaining  in  the  retorts 
or  chambers  of  an  illuminating-gas  plant  after  the  distillation 
of  the  gas.  This  really  is  a  by-product  of  gas  manufacture; 
it  is  soft  and  porous  and  is  of  little  use  except  for  domestic 
heating,  the  manufacture  of  producer  or  water  gas,  and  where 
a  cheap  smokeless  fuel  is  required. 

Domestic,  or  crushed,  coke  is  coke  that  is  crushed  and 
separated  into  sizes — nut,  stove,  egg,  etc. — and  used  for 
domestic  fuel. 

Stock  coke  is  coke  that  is  allowed  to  remain  on  the  yard 
for  some  time,  that  is,  is  stocked  owing  to  scarcity  of  orders 
or  cars.  It  discolors  and  is  thought  by  some  to  deteriorate 
in  quality,  and  sometimes  commands  a  lower  price,  though 
such  coke  is  kept  stocked  a  much  shorter  time  in  the  oven 
yard  than  it  is  in  the  stock  pile  of  a  blast  furnace. 


18 


PRINCIPLES  OF  COKING 


§68 


Soft  coke  is  a  light,  spongy,  large-pored  coke,  produced 
when  heating  the  oven  prior  to  making  good  coke,  or  when 
ovens  are  cold,  or  when  coal  is  not  thoroughly  coked,  or 
when  too  much  air  is  admitted  to  the  oven,  or  in  retorts 
with  a  low  fire. 

Black  ends  are  due  to  imperfect  coking,  to  pulling-  coke 
too  soon,  or  to  a  cold  oven  floor.  Black  ends  may  occur 
in  beehive  or  by-product  ovens,  particularly  in  beehive 
since  the  coal  is  admitted  through  a  tunnel  head  in  the 
center  and  comes  from  the  center  toward  the  side.  Thus, 
the  larger  pieces  of  coal  and  slate  roll  down  the  sides  to 
the  floor  of  the  oven,  and  if  there  is  any  appreciable  quan¬ 
tity  of  slate,  black  ends  will  occur,  or  if  the  oven  is  not 
hot,  the  larger  pieces  of  coal  will  not  be  properly  coked 
through. 

Black  coke  is  coke  that  lacks  the  silvery  luster  of  the 
ordinary  beehive  product  that  has  been  watered  inside  the 
oven  and  is  dark  in  appearance. 

Red  coke  is  coke  that  has  a  reddish  cast  in  places.  This 
is  produced  where  the  ash  contains  much  iron,  or  where  the 
charge  remains  too  long  in  the  oven,  so  that  a  larger  portion 
than  usual  of  the  fixed  carbon  is  burned.  It  is  also  made 
when  the  water  used  in  quenching  the  coke  is  contaminated 
with  sulphate  of  iron. 

Run-of-oven  or  run-of-yard  are  terms  analogous  to 
run-of-mine  coal,  and  refer  to  the  coke  taken  as  it  occurs  at 
the  ovens. 

Hand-picked,  or  selected,  coke  is  coke  in  large  lumps 
selected  for  their  good  appearance  and  quality  and  loaded 
by  hand  to  suit  the  requirements  of  a  particular  customer  or 
for  purposes  of  exhibition. 

Breeze,  screenings,  or  forkings  are  the  small  pieces 
breaking  from  the  larger  lumps  in  drawing  and  handling  the 
coke,  and  which  fall  between  the  tines  of  the  coke  forks 
when  handling  from  the  yard  into  cars.  These  are  gathered 
from  time  to  time,  and  sometimes  screened  to  separate  them 
from  the  fine  ashes  and  brick  dust  and  shipped  to  market  or 
else  made  into  briquets. 


§68 


PRINCIPLES  OF  COKING 


19 


Short  coke  is  coke  occurring  in  short  pieces;  it  is  some¬ 
times  made  purposely  by  coking  shallow  charges  of  coal, 
or  by  coking  coal  in  a  beehive  oven  for  24  hours,  or  less. 


CHEMICAL  AND  PHYSICAL  PROPERTIES  OF  COKE 

30.  Furnace  coke  is  usually  48-hour  beehive  coke,  or 
24-  or  36-hour  retort-oven  coke;  it  must  fulfil  certain  chemi¬ 
cal  and  physical  requirements.  The  essential  element  in 
coke  is  the  carbon,  as  that  is  what  produces  the  heat  when 
the  coke  is  burned;  all  other  elements  contained  in  it  may 
be  considered  impurities.  Chemically,  it  must  not  exceed 
a  certain  maximum  in  impurities,  such  as  ash,  sulphur,  and 
phosphorus,  the  amount  of  the  latter  two  elements  allowable 
depending  largely  on  the  use  to  which  the  iron  made  from 
the  coke  is  to  be  put.  In  smelting  iron  ore  for  Bessemer  pig 
iron,  the  coke  should  not  exceed  10  per  cent,  ash,  1  per  cent, 
sulphur,  and  .02  per  cent,  phosphorus.  The  composition  of 
a  coke  should  be  uniform  to  insure  regularity  in  the  working 
of  the  furnace  and  uniformity  in  the  amount  and  quality  of 
the  iron  produced;  hence,  coke  with  an  excess  of  black  ends 
should  not  be  used  if  it  can  be  avoided,  as  such  ends  are  an 
evidence  that  the  coke  has  been  poorly  made.  The  effects 
of  the  several  impurities  in  coke  are  briefly  as  follows. 

31.  The  ash  has  no  fuel  value,  and  as  the  percentage 
of  ash  increases  there  is  a  corresponding  decrease  in  fixed 
carbon,  necessitating  the  use  of  more  fuel  and  limestone  to 
flux  the  ash.  A  coke  averaging  11  per  cent,  of  ash  and 
varying  only  from  10i  to  lli  per  cent,  is  a  better  blast¬ 
furnace  fuel  than  one  averaging  10  per  cent,  but  varying 
from  7  to  13  per  cent.  The  same  is  true,  in  but  slightly  less 
degree,  as  to  sulphur  and  phosphorus. 

32.  Sulphur  renders  iron  red  short,  that  is,  brittle  when 
hot,  and  even  though  a  part  of  the  sulphur  in  the  coal  is 
removed  in  the  coking  process,  the  coke  may  contain  a 
greater  percentage  of  sulphur  than  the  coal  from  which  it 
was  made,  since  it  takes  usually  about  li  tons  of  coal  to 


20 


PRINCIPLES  OF  COKING 


68 


make  a  ton  of  coke.  A  considerable  part  of  the  sulphur  in 
the  coke  passes  into  the  iron  in  the  blast  furnace;  hence,  the 
amount  of  sulphur  in  the  coke  should  be  made  as  low  as 
possible  by  washing  the  coal  before  it  is  coked,  if  the  coke 
made  from  the  given  coal  would  contain  more  than  the  per¬ 
centage  of  sulphur  allowable  in  a  furnace  coke. 

33.  Phosphorus  renders  iron  cold  short,  that  is,  brittle 
when  cold.  Very  little,  if  any,  of  the  phosphorus  is  removed 
in  the  coke  oven  or  in  the  blast  furnace  or  cupola,  and  prac¬ 
tically  all  of  the  phosphorus  in  the  coke  goes  into  the  iron. 

34.  In  general,  the  analysis  of  a  good  furnace  coke 
should  be  about  as  follows  for  Bessemer  pig  iron: 

Per  Cent. 


Fixed  carbon  .  89.55 

Ash  (including  sulphur  and  phosphorus)  .  9.10 

Volatile  matter  .  .50 

Moisture  .  .85 

Total . 100.00 

Sulphur .  .80 

Phosphorus .  .015 


35.  The  physical  requirements  of  blast-furnace  coke 
are  hardness,  great  crushing  strength,  and  as  cellular  or 
porous  a  structure  as  is  consistent  with  these  qualities.  It 
is  still  largely  held  that  the  bright,  silvery,  semimetallic 
luster  of  beehive  coke  is  essential  to  a  good  blast-furnace 
fuel,  this  gloss  preventing  the  taking  up  of  carbon  by  carbon 
dioxide  (C02  +  C  —  2 CO)  in  the  upper  part  of  the  furnace. 
This  opinion  is  by  no  means  universally  held,  but  reports 
of  blast-furnace  work  show  that  more  retort  coke  (lacking 
the  luster)  than  beehive  is  frequently  required  to  produce  a 
ton  of  pig  iron. 

36.  Foundry  coke  is  supposed  to  be  72-hour  beehive  coke 
or  36-hour  retort  coke;  but  much  of  the  so-called  foundry 
coke  is  ordinary  48-hour  furnace  coke  from  which  the  soft 
pieces  and  black  ends  have  been  thrown  out,  though  often 
even  this  is  not  done.  At  some  coke  plants,  the  only 


§68 


PRINCIPLES  OF  COKING 


21 


distinction  made  between  furnace  and  foundry  coke  is  that 
the  former  is  loaded  into  open  cars,  and  the  latter  into 
box  cars. 

Foundry  coke  properly  comes  in  larger,  longer,  and  harder 
pieces  than  furnace  coke,  and  is  selected  with  more  care  to 
prevent  the  loading  of  soft  pieces  and  black  ends.  A  higher 
price  is  paid  for  this  increased  work  and  time  in  manufacture 
and  handling. 

The  qualities  that  make  a  coke  desirable  for  blast-furnace 
fuel  likewise  render  it  suitable  for  foundry  work.  The  ash 
should  not  be  excessive,  as  it  occupies  the  space  of  fixed  car¬ 
bon.  Sulphur  is  injurious,  as  it  makes  the  iron  hard;  a  portion 
of  it  is  taken  up  by  the  limestone  flux,  if  a  flux  is  used,  but  a 
large  amount  enters  the  iron.  The  amount  of  phosphorus  in 
a  coke  is  seldom  sufficient  to  interfere  with  the  use  of  the  coke 
in  the  cupola,  even  when  making  malleable-iron  castings. 

37.  General  Uses  for  Coke. — Coke,  in  comparatively 
small  amounts,  is  used  for  a  number  of  other  purposes  than 
those  mentioned,  such  as  domestic  use,  fuel  for  locomotives, 
wherever  a  clean,  smokeless  fuel  is  required,  as  in  bakeries 
and  breweries,  and  in  the  manufacture  of  producer  and  water 
gas.  As  a  domestic  fuel,  the  use  of  coke  is  increasing 
rapidly,  particularly  since  the  introduction  into  the  United 
States  of  the  retort  oven. 

Ordinarily,  beehive  coke  or  retort-oven  coke  is  used  for 
domestic  purposes;  but  any  coke  will  answer.  Coke  for 
domestic  use  is  broken  in  rolls  similar  to  those  used  for 
breaking  coal  and  then  screened  to  sizes  known  as  egg, 
stove,  and  nut,  corresponding  to  the  similarly  named  sizes 
of  anthracite. 

The  coke  crusher  is  located  close  to  the  ovens,  and  the 
large  coke  is  generally  loaded  into  small  cars  running  on  the 
coke  yard,  and  hauled  directly  to  an  elevator,  which  hoists  it 
up  to  the  crushing  rolls.  The  final  screened  product  is  col¬ 
lected  in  bins  from  which  it  is  drawn  into  railroad  cars. 

As  ordinarily  fired,  coke  is  an  expensive  fuel  for  domestic 
use.  It  burns  freely  and  produces  an  intense  heat,  so  that 


22 


PRINCIPLES  OF  COKING 


§68 


small  quantities  at  a  time  should  be  added  at  frequent  inter¬ 
vals  in  a  firebox  adapted  to  its  consumption,  and  not  large 
quantities  at  a  time,  as  with  the  slower-burning  anthracite. 
Properly  handled,  however,  it  is  a  very  satisfactory  and 
clean  fuel.  Bakers,  brewers,  and  others  requiring  a  clean, 
smokeless  fuel  usually  buy  stock  or  soft  coke,  because  of  its 
cheapness.  Gas-house  coke  is  also  largely  consumed  for 
this  purpose. 

For  the  manufacture  of  producer  and  water  gas  any  coke 
will  answer,  but  generally  the  smaller  sizes,  such  as  breeze, 
or  forkings,  soft  coke,  and  stock  coke,  are  used.  In  such 
coke,  the  sulphur  is  of  importance,  as  it  cannot  be  removed 
from  the  producer  gas  and  is  consequently  injurious  when 
the  gas  is  burned  in  direct  contact  with  iron.  From  water 
gas  it  can  be  removed  by  passing  the  gas  through  scrubbers, 
which  absorb  the  sulphurous  substances,  but  of  course  at  an 
increased  cost  for  plant  and  maintenance. 


LABORATORY  TESTS  OF  COKE 

38.  Aside  from  the  usual  chemical  analysis  to  determine 
the  percentage  of  impurities  in  coke,  various  tests  may  be 
made  on  the  physical  properties,  the  chief  of  which  are: 
(1)  crushing  strength,  (2)  hardness,  (3)  the  proportion  of 
cells  to  solid  matter,  (4)  capacity  of  coke  to  dissolve  in  hot 
carbon  dioxide,  CO 2. 

39.  Crushing  Strength. — The  crushing  strength  of 
coke  is  usually  determined  on  an  inch  cube  by  some  one 
of  the  various  crushing  machines  made  for  compression  tests. 
Good  coke  has  an  ultimate  crushing  strength  of,  from  1,200 
to  2,200  pounds  per  square  inch,  depending  on  the  coal  from 
which  it  is  made  and  the  process  by  which  it  is  coked. 

40.  Hardness. — The  hardness  of  a  coke  is  that  of  the 
materials  forming  its  cell  walls,  and  for  good  furnace  fuels  is 
about  2.5.  It  is  determined  by  the  usual  methods  of  miner¬ 
alogy  or  by  placing  a  cube  of  coke  at  a  fixed  pressure  against 
an  emery  wheel  revolving  at  a  known  rate  of  speed.  The 


§68 


PRINCIPLES  OF  COKING 


23 


loss  in  weight  of  the  sample  in  a  given  time  serves  as  a 
basis  for  comparison  with  other  cokes. 

41.  Percentage  of  Cell  Space. — The  percentage  of 
cell  space  in  good  cokes  varies  from  44  to  56,  and  the  deter¬ 
mination  of  this  percentage  requires  care.  A  cube  of  con¬ 
venient  size,  say  1  cubic  inch,  is  prepared  representing  a  fair 
section  of  the  coke,  carefully  brushed  from  all  adhering 
particles,  heated  to  expel  moisture,  cooled,  and  weighed  in 
air.  The  same  cube  is  then  soaked  in  water  under  the 
receiver  of  an  air  pump  until  the  pores  of  the  coke  are 
thoroughly  filled  with  water,  and  then  weighed.  From  the 
specific  gravity  of  the  solid  portion  of  the  coke,  not  including 
the  cell  space,  and  the  weights  of  a  cubic  inch  of  the  coke  in 
its  natural  form,  when  dry,  and  when  saturated  with  water,  it 
is  possible  to  calculate  the  percentage  of  cell  space  in  the 
coke.  For  example,  if  1  cubic  inch  of  coke  when  dry  weighs 
15  grains,  and  when  saturated  with  water  weighs  23  grains, 
the  coke  has  absorbed  8  grains  of  water;  that  is,  in  the 
coke  there  is  sufficient  space  to  hold  8  grains  of  water.  If 
the  specific  gravity  of  the  solid  portion  of  the  coke  is 
1.75,  a  volume  of  coke  equal  to  this  space  will  weigh 
8  X  1.75  =  14  grains.  Therefore,  a  piece  of  solid  coke 
would  weigh  15  +  14  =  29  grains.  It  follows,  therefore,  that 
the  actual  weight  of  coke  multiplied  by  100  and  divided  by 
the  weight  of  the  coke,  if  it  were  solid,  gives  the  percentage 
of  solid  coke  in  the  mass;  and  the  weight  of  coke  lost  by  the 
cellular  structure  multiplied  by  100  and  divided  by  the  same 
factor  gives  the  percentage  of  cell  space. 

In  the  present  case, 


Coke  or  body  . 


Cells 


42.  The  specific  gravity  of  the  coke  may  be  deter¬ 
mined  approximately  as  follows,  or  more  accurately  by  any 
of  the  well-known  methods  of  determining  the  specific 
gravity  of  a  substance. 


24 


PRINCIPLES  OF  COKING 


68 


Let  a  =  weight  of  dry  coke; 

b  =  weight  of  water  it  can  absorb; 
c  =  loss  in  weight  in  water  of  coke  saturated  with 
water; 

x  —  specific  gravity  of  solid  part  of  coke. 

Then,  (c  —  b)  :  a  =  1  :  x 


Example. — A  piece  of  dry  coke  weighs  20  grains,  but  when  satu¬ 
rated  with  water  it  weighs  30  grains  when  weighed  in  the  air,  and 
only  8  grains  when  weighed  in  water,  (a)  What  is  the  specific  gravity 
of  the  coke?  (£)  What  is  the  percentage  of  cell  space?  ( c )  What  is 
the  percentage  of  solid  coke? 


Solution. — (a)  By  applying  the  formula  for  the  specific  gravity, 

a  20  20  i  a 

X  c  -  b  22  -  10  “  12  “  1'66'  AnS‘ 

(b)  The  weight  of  coke  equivalent  to  the  cellular  space  is  1.66  X  10 
=  16.6  gr.;  if  solid,  the  coke  would  weigh  16.6  +  20  =  36.6  gr.  The 
amount  of  cell  space  is 


16.6  X  100 


36.6 

(c)  The  amount  of  solid  coke  is 
20  X  100 
36.6 


=  45.36  per  cent.  Ans. 


=  54.64  per  cent.  Ans. 


43.  Capacity  of  Coke  to  Dissolve  in  Hot  Carbon 
Dioxide. — A  weighed  quantity  of  coke  is  tested  in  a  tube  in 
a  current  of  hot  carbon  dioxide,  and  the  issuing  gas  is 
analyzed  for  its  percentage  of  carbon  monoxide;  or,  the  coke 
remaining  in  the  tube,  is  weighed  after  the  test.  In  the  first 
instance,  the  percentage  of  carbon  monoxide  in  the  issuing 
gas,  and  in  the  second  the  loss  in  weight  of  the  coke,  indi¬ 
cates  the  solvent  effect  of  carbon  dioxide  on  the  coke  in  the 
charge.  Good  furnace  cokes,  when  subjected  to  the  first  test, 
give  a  gas  showing  a  little  more  than  5  per  cent,  of  carbon 
monoxide;  and  when  submitted  to  the  second  test,  they  show 
but  little  loss  in  weight. 

44.  Field  Tests  of  Coking  Coals. — The  only  certain 
test  of  the  coking  qualities  of  a  coal  is  to  try  it  in  a  coke 
oven,  and,  whenever  possible,  an  amount  of  coal  sufficient  to 


§68 


PRINCIPLES  OF  COKING 


25 


give  one  or  more  complete  tests  should  be  shipped  to  a 
coking  plant  and  there  tried.  If  the  coke  fails  to  coke  in  the 
beehive  oven,  it  should  then  be  tested  in  the  retort  oven. 


PREPARATION  OF  COAL  FOR  COKING 

45.  Necessity  for  Preparation. — Good  coking  coals, 
unless  high  in  sulphur  or  extremely  slaty,  require  no  especial 
preparation  for  coking,  except  that  they  should  be  broken  up 
into  reasonably  small  fragments.  Although  the  best  coke 
can  be  obtained  by  first  sizing  the  coal,  this  is  not  always 
necessary  or  practicable.  In  soft  or  friable  coals,  like  those 
of  the  Connellsville  region  of  Pennsylvania,  the  coal  is 
broken  and  sized  sufficiently  in  the  mining  and  by  the  subse¬ 
quent  loading  into  the  mine  cars,  dumping  into  the  coal  bins, 
drawing  from  the  bin  into  the  larries,  and  the  final  charging 
and  leveling  in  the  coke  oven.  In  mining  this  coal,  a  pick 
is  used  and  the  cutting  is  distributed  evenly  over  the  entire 
face  of  the  working  place,  or  room,  that  is  being  excavated. 
The  larger  pieces  of  coal  occasionally  produced  are  broken  by 
hand  before  being  loaded  into  the  mine  car.  When  coals  are 
hard,  particularly  where  they  are  not  rich  in  volatile  matter 
(containing  less  than  32  per  cent.),  the  lumps  must  be 
crushed  in  order  to  be  successfully  coked.  If  the  lumps  are 
too  large,  the  heat  of  the  oven  will  not  penetrate  to  their 
centers  and  the  outside  of  a  lump  will  be  coked  while  the 
center  will  be  found  to  contain  raw  coal.  Large  lumps  also 
consume  too  much  time  in  coking  and  tend  to  retard  the  proc¬ 
ess.  When  large  and  small  pieces  occur  in  the  same  charge, 
the  coking  of  the  lumps  will  necessarily  consume  much  more 
time  than  is  required  by  the  fine  portion  of  the  charge. 
Uniformly  sized  material  cokes  or  burns  downwards  at  a 
regular  rate,  until  the  bottom  of  the  oven  is  reached,  when 
the  process  should  be  complete.  Coke  produced  from 
crushed  coal  is  more  uniform  in  texture  and  can  be  drawn 
from  the  ovens  in  larger  pieces  than  coke  made  from 
uncrushed  coal.  The  larger  pieces  of  slate  may  be  removed 
by  screening  and  washing.  Coke  made  from  crushed  coal 


26 


PRINCIPLES  OF  COKING 


§68 


presents  a  better  appearance  than  that  made  from  uncrushed 
coal,  as  its  structure  shows  no  large  pieces  of  slate,  as  is  sure 
to  be  the  case  when  the  coal  is  not  crushed.  The  practice 
of  crushing  coal  for  the  manufacture  of  coke  is  gradually 
*  being  adopted  in  many  parts  of  the  United  States  and 
Canada.  The  machines  used  for  crushing  the  coal  prior  to 
coking  are  the  same  as  are  used  in  crushing  it  prior  to 
washing;  but,  as  a  general  rule,  when  the  coal  is  crushed  but 
not  washed  the  crushing  is  carried  to  a  much  finer  degree. 

46.  The  practice  of  washing  coal  that  is  to  be  coked  to 
reduce  the  amount  of  sulphur  and  ash  in  the  resulting  coke 
is  steadily  increasing.  Experiments  have  shown  conclusively 
that  not  only  can  the  value  of  the  coke  be  increased  by  first 
washing  the  coal,  but  that  certain  coals  that  do  not  coke  with¬ 
out  washing  can  be  coked  after  the  excess  of  slate  has  been 
removed  by  washing.  The  methods  of  crushing  and  wash¬ 
ing  coal  are  fully  explained  in  Coal  Washhig. 


PRINCIPLES  OF  COKING 


EXAMINATION  questions 

(1)  What  is  coke? 

(2)  What  is  meant  by  the  by-products  of  the  coking 
process? 

(3)  For  what  is  coke  used? 

(4)  (a)  By  what  processes  is  coke  made?  (b)  For  what 
is  the  open-pit  method  of  making  coke  mainly  used? 

(5)  What  is  meant  by  the  term  coking  coal? 

(6)  What  is  meant  by  the  cement  or  binder  of  a  coking 
coal? 

(7)  How  can  some  so-called  non-coking  coals  be  made  to 
coke? 

(8)  What  effect  has  the  amount  of  moisture  in  a  coal  on 
its  coking  properties? 

(9)  Does  the  amount  of  ash  in  a  coal  affect  its  coking 
qualities? 

(10)  Has  the  amount  of  sulphur  and  phosphorus  in  a  coal 
any  effect  on  its  coking  properties? 

(11)  What  becomes  of  the  sulphur  in  a  coal  when  the 
coal  is  coked? 

(12)  What  effect  have  lime  and  feldspar  when  mixed  with 
a  coking  coal? 

(13)  Has  the  geological  position  of  a  coal  bed  any  effect 
on  the  coking  properties  of  the  coal  in  the  bed? 


§68 


2  PRINCIPLES  OF  COKING  §68 

(14) '  Why  should  coals  be  crushed  before  they  are  coked? 

(15)  What  is  meant  by  the  term  theoretical  yield  of  coke? 

(16)  Calculate  the  theoretical  yield  of  coke  from  a  coal  of 
the  following  analysis,  coked  in  a  beehive  oven: 


Per  Cent. 

Moisture .  2 

Volatile  combustible  matter .  30 

Fixed  carbon .  60 

Ash .  8 

Total .  100 


Ans.  68  per  cent. 

(17)  Why  is  it  possible  to  obtain  more  than  the  theo¬ 
retical  yield  of  coke  when  coal  is  coked  in  a  retort  oven? 

(18)  If  the  theoretical  yield  of  coke  is  50  per  cent,  of  the 

weight  of  the  coal,  how  many  tons  of  coal  will  be  required 
to  produce  a  ton  of  coke?  Ans.  2  T. 

(19)  (a)  How  may  the  approximate  percentage  of  ash 
and  phosphorus  in  a  coke  made  from  a  given  coal  be  calcu¬ 
lated?  ( b )  How  is  the  percentage  of  fixed  carbon  in  the 
coke  obtained? 

(20)  What  are  the  principal  varieties  of  coke? 

(21)  What  are  the  requirements  of  a  good  furnace  coke? 

(22)  For  what  are  the  principal  laboratory  tests  made  on 
the  physical  properties  of  coke? 

(23)  How  are  coals  prepared  for  being  charged  into  the 
oven? 


SUPPLIES  FOR  STUDENTS 

In  order  to  do  good  work,  it  is  very  necessary  for  our  students  to  secure  the  best 
materials,  instruments,  etc.  used  in  their  Courses.  We  have  often  found  that  inex¬ 
perienced  students  have  paid  exorbitant  prices  for  inferior  supplies,  and  their  progress 
has  been  greatly  retarded  thereby.  To  insure  our  students  against  such  errors,  arrange¬ 
ments  have  been  made  with  the  Technical  Supply  Company,  of  Scranton,  Pa.,  to  furnish 
such  as  desire  them  with  all  the  supplies  necessary  in  the  different  Courses.  The  supplies 
listed  below  are  first  quality  and  the  prices  are  reasonable. 


LIGHT-WEIGHT  ANSWER  PAPER 

RULED— Size,  8*'  X  14"  Price 

500  Sheets* . . ./ .  SI. 50 

500  Sheets! .  2.25 

250  Sheets* . 75 

250  Sheetsf..... . .  1.15 

100  Sheets! . 45 

Sample  sent  on  application 

“T.  S.  CO.”  COLD-PRESSED  DRAWING  PAPER 

Size,  15"  X  20" 

24  Sheets  (one  quire)* . 90 

24  Sheets  (one  quire)! . . .  1.14 

Smaller  Quantities,  5  Cents  per  Sheet! 

Sample  sent  on  application 

PORTFOLIOS 

!For  holding  Drawing  Plates,  size  14"  X  18" .  2.00 

!For  holding  Answer  Paper,  size  9"  X  14 ¥ . 75 

“T.  S.  CO.”  WATERPROOF  LIQUID  DRAWING  INK 

Per  Bottle! . 25 

FOUNTAIN  PENS 

“T.  S.  Co.”  14-karat  Fountain  Pen .  1.00 

I.  C.  S.  Special  Fountain  Pen,  Fully  Guaranteed .  2.50 

DICTIONARIES 

Webster’s  Practical  Dictionary! . 1.00 

Webster’s  Collegiate  Dictionary*  (full  sheep) . 4.00 

RUBBER  HAND  STAMPS 

Rubber  Hand  Stamps,  with  Ink  Pads,  containing  name  and  address, 

also  class  letter  and  number  of  a  student,  each! . 50 

DRAWING  OUTFITS 

Complete  Drawing  Outfit,  No.  1;  Arts  and  Crafts  Drawing  Outfit; 
Lettering  and  Sign  Painting  Outfit;  Chart-Work  Drawing  Outfit; 
Show-Card  Writers’  Outfit,  each .  13.55 


Description  of  above  Outfits  mailed  on  application.  Students  of  the  International  Corre¬ 
spondence  Schools,  holding  special  Privilege  Slips,  may  purchase  these  Outfits  at  Special  Prices. 

CATALOGS 

ANY  OF  THE  FOLLOWING  CATALOGS  WILL  BE  MAILED  FREE  ON  APPLICATION 

Drawing  Instruments  and  Materials.  Fine  Tools.  Practical  Books 
Relating  to  Architecture  and  Building  Trades.  Practical  Books  Relating 
to  Civil  Engineering.  Practical  Books  Relating  to  Electricity.  Practical 
Books  Relating  to  Mechanical  and  Steam  Engineering.  Practical  Books 
Relating  to  Mining,  Metallurgy,  and  Chemistry. 

*By  Express,  not  paid.  fBy  Mail,  postpaid 


Order  through  TECHNICAL  SUPPLY  COMPANY,  Scranton,  Pa. 

NOTE. — The  above  prices  are  for  students  in  the  United  States  only.  Foreign 
students  should  purchase  from  the  agents  in  charge  of  their  territory.  An  additional 
charge  covering  duty  and  freight  must  be  prepaid  on  material  purchased  direct  from 
the  Technical  Supply  Co. 


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